For pt.I see ibid., vol.50, no.3, p.267-78 (2003). This paper presents an application of continuous wave ultrasound Doppler velocity measurements to two-phase flow in pipes. In many petroleum wells, ...the multiphase flow is separated into two phases: the first is a liquid phase and the second is a gas phase with small scatterers. The problem of multiphase velocity profile measurements has not been satisfactorily solved by classical approaches due to the multiphase nature of the fluid and the presence of colored noise, which introduces a significant bias in classical frequency estimators. We propose the use of resolution frequency techniques to overcome the classical limitations. Direct estimation of Doppler frequency then obtained using either time frequency maximum frequency or arguments of poles of the parametric model that identifies the Doppler part of the signal is discussed. The tests made with synthetic Doppler signals and two-phase flow have demonstrated the excellent performance of the high resolution techniques based on reassignment and parametric techniques.
We compare several techniques to evaluate the frequency shift related to the attenuation phenomenon. More precisely, we compare the short time Fourier analysis and the short time autoregressive ...analysis to new techniques based upon the Wigner-Ville transform with parametric and non parametric approaches. In the parametric methods, we propose a new frequency estimator called the mean resonating frequency. All of these methods are evaluated in terms of relative error and standard deviation of the attenuation estimation.
It is well known that classical time delay estimation gives an inexact estimation of the true delay between two signals delayed by non integral multiple of the sample period. For more accurate ...estimation, new methods are proposed to estimate small time delay with regard to the sample period of ultrasonic signals. In this paper, we focus on two methods based on the wavelet transform for time delay estimation between an ultrasound emitted pulse and the received signal. The first technique consists of computing at a fixed frequency (which is the emitting frequency of the ultrasonic signal) the difference of maximum time argument between wavelet coefficients of the two signals (the reference and the delayed signal). The second technique, based on a crosswavelet representation, directly provides the time delay between the two signals. The performance of these methods in terms of bias and variance are compared to classical correlation using polynomial interpolation. Numerical results show the superior performance of the crosswavelet approach for time delay estimation.
PDF
